In recent years, owing to a concern for power shortage and a request for global environmental protection, each store, household, building, and the like (hereinafter abbreviated as each store and the like) have been asked for power saving. A power demand increases especially in summer time and winter time, and a power consumption by each store and the like sometimes exceeds a contract demand. As such, in order to effectively save power and prevent the power consumption from exceeding the contract demand, what is called BEMS (Building and Energy Management System) that monitors the power consumption of each store and the like and controls the power consumption of various electrical products (hereinafter, referred to as a power load) has been proposed. In the BEMS, a power sensor detects the power consumption of each power load and transmits data associated with the detected power consumption to, for example, a remotely located server. Then, the server, while monitoring the power consumption, transmits a control signal according to the power consumption to each power load, thereby efficiently reducing the power consumption of each power load.
Here, when an amount of data from a power sensor increases in proportion to an increase in the number of power loads, a traffic load for data transmission to the server and a server load also increase. As a result, the data acquired by the power sensor are not transmitted to the server within a predetermined time, inhibiting control in accordance with a current power consumption.
As such, there has been proposed, for example, a method of reducing the amount of data when the traffic load is increased and sending a reduced amount of data (for example, see PLT 1). According to the method described in JP 2000-216932 A, the transmission apparatus, prior to the data transmission to a reception apparatus (a server), acquires information about the traffic load on a network. Then, when the traffic load according to the information thus acquired is greater than a predetermined value, the transmission apparatus changes a data attribute (resolution and the like) in order to reduce the amount of the data and transmits the data in a reduced amount.